A mat such as is cut up and spun into yarn or of the type used in filters or diapers, or as insulation, is typically made from lint-like fibers. These fibers are delivered at random to the upper end of an upright and horizontally elongate supply duct in which they are distributed and fall as a ribbon-shaped web. At the lower end of this duct the the web passes out, normally between two feed rollers, into the upper end of a forming duct that is also horizontally elongated and that extends parallel to the supply duct.
Baffles are normally provided in the supply duct to distribute the fibers uniformly therein over the entire width of the duct, the width being measured perpendicular to the longitudinal direction of the web across its greatest transverse dimension. This is done to make the thickness of the web uniform, the thickness being measured transversely both to the width and to the longitudinal direction across the workpiece.
Such an arrangement often is inadequate to compensate for a partial blockage of the feeding device, or other anomalies that might affect workpiece thickness. Even if the baffles are adjusted and rearranged to compensate for some workpiece fault, it is fairly common for a new problem to develop which creates a longitudinal groove or ridge in the workpiece.